Medullary respiratory neuronal activity during augmented breaths in intact unanesthetized cats.

In intact unanesthetized cats, we studied the behavior of five medullary respiratory cell types during augmented breaths: 1) decrementing, 2) augmenting, and 3) late-onset inspiratory cells and 4) decrementing and 5) augmenting expiratory cells. Certain features of their behavior were inconsistent with either their proposed role in rhythmogenesis or the proposed nature of augmented breaths. For example, decrementing inspiratory cells switched to an augmenting pattern during the second part of the augmented breath. This behavior is inconsistent with mechanisms proposed to account for their decrementing pattern and with their postulated inhibitory actions on augmenting inspiratory cells, which are intensely active at the same time. In addition, augmenting expiratory cells discharged intensely at the end of inspiration and then throughout expiration, indicating that their discharge profiles (and, therefore, their inhibitory actions) are more labile than previously assumed. The behavior of inspiratory cells gave mixed evidence of the idea that the augmented breath comprises two inspiratory phases: decrementing and late-onset inspiratory cells discharged in two bursts during the inspiratory phase, but other inspiratory cells discharged without interruption throughout it. These results reveal that current theories do not account for the behavior of medullary respiratory cells during augmented breaths.